1. Field of the Invention
The present invention relates to improvements in a protective device for a liquid spraying apparatus.
2. Description of the Prior Art
U.S. Pat. Nos. 3,963,180 and 4,036,438 disclose spraying apparatus.
An exemplary conventional spraying apparatus as illustrated in FIGS. 9 and 10 comprises: a main housing 1, an electromagnetic driving unit 2 fixedly attached to the main housing 1, a grip 3 depending from the rear end of the main housing 1, a switch 4 held on the grip 3, a pump housing 1A fastened to the front end of the main housing 1 with screws 5, a cylinder 6 horizontally extending within the pump housing 1A, a piston 7 inserted from the rear end into the interior of the cylinder 6, a coil spring 8 interposed between the cylinder 6 and the piston 7 to resiliently bias the piston rearward, a cap 9 formed integrally with the pump housing 1A at the lower end of the pump housing 1A and provided with an internal thread 11, a container 10 for containing water, paint or the like, screwed on the cap 9, a suction pipe 14 fitted at the upper end thereof in a suction hole 12 extending through the pump housing 1A and the cap 9, a strainer 15 enclosing the suction opening of the suction pipe 14, a valve assembly including a valve 17, a coil spring 18 and a swirl chip 24 and attached to the front end of the pump housing 1A, a nozzle head 19 attached to the front end of the valve assembly, a conical protective cover 16 screwed on the nozzle head 19, a housing cover 1B fixed to the main housing 1 with screws 20 so as to cover the electromagnetic driving unit 2 and other parts provided within the main housing 1, and an adjusting screw 21 screwed into the main housing 1 and biased with a coil spring 22. The switch 4 is closed to apply an AC voltage to the solenoid 2A, and thereby the armature 2B of the electromagnetic driving unit 2 vibrates in horizontal directions. The piston 7 is reciprocated within the cylinder 6 by the combined action of the vibration of the armature 2B and the resilience of the coil spring 8. A discharge hole 13 is formed through the pump housing 1A and the cap 9. The amplitude of vibration of the armature 2B of the electromagnetic driving unit 2 can be adjusted by adjusting the gap between the front end of the adjusting screw 21 and a stopper 23 by turning the adjusting screw 21.
When the electromagnetic driving unit is energized, the armature 2B of the electromagnetic driving unit 2 is vibrated within the gap between the adjusting screw 21 and the stopper 23. The piston 7 is reciprocated within the cylinder 6 by the combined action of the coil spring 8 and the armature 2B. The liquid, such as water or paint, contained in the container 10 is sucked through the suction pipe 14 into the cylinder 6 by the reciprocation of the piston 7 during the suction stroke of the same. The liquid thus sucked into the cylinder 6 is compressed during the compression stroke of the piston 7 to open the valve 17 forcibly against the action of the coil spring 18, and thereby the liquid is sprayed through a nozzle hole 26 formed in the front wall 25 of the nozzle head 19.
This spraying apparatus jets the liquid through the nozzle hole 26 of the nozzle head 19 at a high pressure to form a high-pressure region in the vicinity of the nozzle hole 26. Therefore, it is possible that the hand is injured by a high-pressure jet of the liquid, when the hand is put accidentally into the jet of the liquid in the high-pressure region. In order to prevent such a danger, a protective cover 16 is provided so as to surround the nozzle hole 26, as shown in FIG. 10.
The protective cover 16 is formed in a skeleton framework so as to surround the jet of the liquid and to allow air to flow therethrough into the interior space thereof, and is provided with an air passage 26 to supply air to the jet of the liquid so that the jet of the liquid is sprayed without touching the inner surface of the protective cover 16. However, when the liquid is jetted out through the nozzle hole 26, a negative pressure is produced inside the protective cover 16 around the jet of the liquid, and thereby the liquid is caused to adhere to and drip along the inner surface of the protective cover 16.